Cd1−xFexSe room temperature fundamental reflectivity in 4–10 eV energy range

0038-1098/89$3.00+.00 Pergamon-Press plc

Solid State Communications,Vol. 70, No. 7, pp. 693-698, 1989. Printed in Great Britain.

Cd ,_XFeXSe ROOM

TEMPERATURE

FUNDAMENTAL

REFLECTIVITY

IN 4-10 eV ENERGY

RANGE

A.Kisiel Instytut Fizyki, Uniwersytet Jagiellonski 30-059 KrakOw, Reymonta 4, Poland M. Piacentini Dipartimento di Energetica Universita di Roma la Sapienza, Roma,

Italy

F.Antonangeli, N.Zema Istituto di Structura della Materia CNR 00044 Frascati, via E-Fermi 38, Italy A.Mycielski Instytut Fizyki, Polska Akademia Nauk 02-688 Warszawa, al. Lotnikbw 32/46, Poland (Received

15 September

The

reflectivity

of

blurring observed.

Se

therefore

II-VI mixed

very

exciting

of

their

of

the

better

( DOS

The

Fe2+

state

ion

gap about maximum

0.6

degenerated in

the

state the

the

of

HgFeSe

configuration

into

the

(r3) and Because above

two an of

excited

states

deep

ion

term.

expressed

band

(EDC)

band

in

approach,

0.3

distribution

ternary

valence features below

The

first

one

is similar

peak

in

non

by

two

et

3.5 eV and 0.2 VBM

[4].

Mn-based rather

pure

zero

second

feature

171,

DMS 3d

position

with of

are Fe the

to a corresponding spectra

associated

orbital was

which

al.161

photoemission

both

693

Wall energy

the

show

region

about the

curves

compounds

band

content.

5E

are and

integrated

In

ground

state

angularly

correlated

the

the

respectively,

electron

splits

for the 2),

(t29)3te4)3

energy

eV

=

electrons,

for HgFeSe

additional -

still (S

excited

from

the

is

[4], or considering

and first

photoelectron

is

ground

between by

state

it

of the 'T, in Es

configuration

The

possessing

5T,(r',) state

interaction

density

elements

matrix

constructed r51.

state

D term

: a

ground

the

energy

The

spin 5

and

the top of

band

a contribution

electron

tt,g)4(eg)2

valence

[3].

the

near

valence

spin

donor

conductivity

5D

orbitals

and vice versa

[1,2].

Mn

this

components

the

from

forbidden

in high

is

state

semiconductors

free

structure

expected

high

the

interaction

3d

off-diagonal a

an one

large

of DMS with

Fe2+

and

class

in the

3d6 electrons

tetrahedral

a new

a

were

).

These

as

step

features

feature

1 in the

to the

for CdFeSe;

the

( VBM

properties.

with

case of

an additional

Fe

0.15)

A two

stronger

and

because

eV above

(VBM)

a

5p

0.10,

studied.

spectra

about Cd

1989 by P.Burlet)

(x = 0.00,

been

studies

appears

localized

then

maximum

significantly

group

inform

3d

semiconducting

magnetism

differ known

band

have

reflectivity

it is expected

of

belonging

range

results Fe

form 3 February

of Cdl_XFeXSe

CdFeSe

and

Fe are

field

diluted

(DMS),

4p

binary with

unique

materials,

the

valence

of states

The

spectra

Above

between

the

in revised

4 - 10 eV energy

in the

compounds

1988,

with

character.

related

to hybrid

of a The p

vol. 70, No. 7

Cdl_xFexSe ROOM TEMPERATURE

694

- 3d

orbitals

occurring

near

the top or

VBM. The of

aim

of

reflectivity compounds

spectra

materials

Sarem

et

al.

They

to lower

been

in

1

by

us

using

the

were

in

of

the

entire

and

of

the

at

Polish

Warsaw

by

method

[31.

by x-ray lattice the

content

The

samples

were

was checked

spectra

on

between

compounds

the

4

and

comparison, of

CdSe.

b

5.50

zoo

10.00

8.50

E IeVl

Cd ,_,FeXSe in

spectra

4 - 10 eV

reflectivity the main F ,,

spectrum

structures

E,,

of

energy

almost

vector The

of

samples

etched

in 2%

alcohol.

The

surfaces

F,

range.

eV

for

two

ternary

) and, for the

CdSe

E,A,, E,A2, E,B,

notation

[lo].

is elliptically

full the

linear axis

between c

axis

of

of

Because

the

the

contribution Such

manifest Fig.11,

the

beam

angle

and

crystal

exist

the

amounts

some

; II ;

identified

experimental

small

transitions.

is

likely

by us as

features,

to

transitions and volume

results

all

and

selected

Bergstresser

Oull.

CdSe

[9,101

estimations at

E,B and E'

for

with results

regions

(see

respectively.

Bergstresser

theoretical

at

in this experimental

of the

experimental

(BZ).

and

light

oriented

( a

only

in the C and D structures

("c 11 H,

with

exists

contribution

a

synchrotron

polarized

)

beam

incident

Cardona's

of

polarization

the

indicated

using

radiation

satisfactorily

reflectivity

we have

as

and

E;

could

reflectivity In

E;

degrees,

10

the

F, E2

to several

( x = 0.10 and 0.15 also

D

conditions

Cd *_xFexSe

of

C

for

diagnose.

the

I

the

reflecting x-ray

4.00

t

of

electric

and

of

chemical

G-axis

the

E,B

tt

performed

(G 1 g).

the

using

compositions

spectrum

with

presents

Fig.1

Bridgman

of the

polished

of

in

the dependence

of Br, in methylic

orientation

study

measurements

to the

cleaved,

solution

0.10

Physics

measurements

light

The

defined

of light were

E:,A

t

Fig.l.Reflectivity

was

parameters

incident

[91.

Sciences

Fe

perpendicular the

of

using

L

t

average

of

The

diffraction

2’

ADONE

present

a modified

reflectivity oriented

the

Institute

of

composition.

the

structure

means

lattice

of

I-2A

range

Academy

constant

the

( x = 0.00,

in

the

at

Frascati

wurtzite

1 used

grown

with

the

The

of Cdl_XFeXSe

0.15

shift

by the

was

energy

monocrystalline

0.0

the

Faci!ity

INFN

set-up

0.10

studies

line

the

Laboratories.

were

The

Radiation

resolution

samples

large

beam

at

by

in

for

radiatiol. emitted

ring

the

energy

performed

National

over

out

6 eV

a broadening

accelerated

electrons

for

-

reported

and

Synchrotron

storage

study

reflectivity

and

ultraviolet

Italian

energy

carried

content.

Fe

mixed

eV

similar

has

energies

reported

10

E, a relatively

increasing

vacuum

a

light

study

fundamental

-

measured

signed

PULS

4

ISI

nonpolarized

is the

of Cdl_XFeXSe

the

in

these

range.

work

temperature

Recently

range.

peak

this

room

the

agree

previous as

well

of the interband critical

points

of the Brillouin and

as Cl21

Cohen

Cohen

[121

zone the

which

calculations particularly positions

of the valence

recent

Kobayashi

valence

range

and of

z-dependence

from

the

BZ

energies

light.

zinc

blende

tetrahedral

coordination,

surrounded

by

are

the

then

the

substitute case

CdFeSe,

the

lower

space

Fe

wave

3d

stressed

by

Kobayashi

bands

p-like

orbitals

contribution

valence

point

very we

and

the

at saddle

s

high

points

DMS the

the

is

the

"sizable" and

to

the

the

p-like I point

should

expect a more 2+. of the Fe ions on

symmetry

in the

volume

on the

edge

near

the

r

E(x)

of

the

common

of the

to

C of

our

blurring

should

near

observed

the

VBM

of b

position

Table

the

of

I.

A

interband top

of

us 4p

on and in

as an

similarly

for HgFeSe

a

of

appear

spectrum

a

Mn-based

reflectivity

in

Se

of

is

all

CdSe

informs

hybrid.

photoemission

linear

positions

and

the

the

content A

of the slope

to

of

It

Fe

t b.

almost

of

close

the

in

( 0 5 x 5

with

listed

band

of

maxima

ax

q

in

localization

feature

the

that

positions

to the energy

are

transitions

been

much

as

structures

structures

spectrum)

is

a contribution

lines

(corresponding

speedy

F,,E,

energy

to

straight

the

with

blurring

suggestion

linearly

[161. The values

valence

constructed

anion

near

p-like

known

transitions

of the BZ than

5p

been

Cd

speedy the

composition

reflectivity

property

E: around

or

H 2 transitions

of

to

dependence the

and

to the r point

energy

shift

of

[131

a

well

influence

interband

al.

by

structure

Therefore

significant the

is

from

only

0.15)

according

of

of the C and D

reflectivity

range

metals

from the anion

cation

it

band

orbitals

and

of As

prevalently

et

The

studied

1, ES].

in Table

these

are

G

top

spectrum.

Cd i_XFexSe

in the a

very but

E,B,

our

structures

reflectivity

has

has

close

the

E,A, at

blurring

supports

D

mixed

between

are created

It

not

results

and

E,AI,

identifies

transitions BZ.

are

reflectivity

in Fig.1

transitions

structures

the

transitions

A speedy

selected

expect

As

the

and

CdFeSe

CdFeSe

are blurred

the

for Cd 5p because

overlap

of

by

1163.

from

for

of Fe content

and

Fe '+ 3d and

functions.

valence

orbitals.

should

increase

vice

As

ternary

between

the r point

distant

therefore

we

than

and

more

as

of the

also

occupied

supports the

the

( ES transition

structures

identified

to

also

presented

The

and

respectively

band

of

is

themselves

transition and

interaction

Se 4p orbitals

and

for

in DMS

cations

of

stronger

[151.

cations

the

compounds

have

surrounding.

1141

for

anion

I.

a shift

transition

reported

analysis

by

modifications

the

statement

slower.

wurtzite

every

neighbours

anion

reported

results

which

cations

second

their

been

four

available

and

structures,

points

In Table

all

CdSe.

crystalline

but

spectra

high

and experimental

versa,

final

1 for

theoretical In

an

point

compared

was

steep

relatively

incident

and

of

valence

a

optical

above

subject

This

and

states,

of the

10

the

( r

for

eV

3d

course

as

expressed

points

from

Fe

-

critical

center

of the

listed

the

conductivity

Hove

observed

4

show

that

in Van

are

I are

the

a

be

critical

transition

Of

can

of the bands,

Hove

empty

start

in

also

causes

It

transitions far

which

from

deformation Van

[I31

highest

the

influence

more

electronic

of

transitions

bands.

with

al.

demonstrate

system

bands

interband

CdSe

bands

et

calculations flat

energy

and the energy

tight-binding

semiempirical

This

well

rather

agree

in the shape

structure

structure

band

method

pseudopotential

rather

695

CdI_xFe,Se ROOM TEMPERATURE

Vol. 70, No. 7

the the

Fe

3d

CdFeSe

additional

to

what

has

of

the

[5].

directions regions of the

If to consider

or BZ.

a)

a different

rate

of

blurring

696

CdI_xFexSe ROOM TEMPERATURE Table

Energy

Bergstresser

and identification

interband

transitions

and Cohen

Cardona

Transit.

M,c.p.at

rs - F3

i4 .l d Ident

ii: 1 d

$1:

[ eV1

[ eV] Ident

[ eV] Ident*

4.07

A,

4.18

4.30

A2

E,B

4.82

4.30

levels

1.14

B

5.00

E,B

4.73

0.36

--

E;

6.01'

_-_

__

D

6.23"

0.71

Ml

6.20

F,

6.80

---

--

F,

7.02

0.93

K2

7.10

E,

7.55

---

--

E2

7.50

0.21

7.90

E;

8.35

---

--

EI

8.42

-1.5

-_

Fs

9.20

---

--

F,

9.10

0.50

M2

-

K, F

_ F

5

6

---

positions

of transitions

structures the

to

CdFeSe

in

localization

transitions

of

a

forbidden

Fe'+deep gap

of

can

donor

reported

states

one

the

CdFeSe

including

in

an

B

related

of

be

and

C

one

should

of

s-p

(see

seem

hybridized 3d

and

orbitals

expected

features DOS

be

Se

C and A features

Recently,

in

The

the

Fe

A

band

by

CdMnTe.

Fig.2

to

but

proposed

for

in

a contribution

valence

as

[71

shown

respectively. B,

like al.

mainly

nonhybridized

in

the

Fig.2)

by

us

CdFeSe

have

been

studies

photoemission

r171.

Fig.2, In

band density

the

et

discovered

compounds

from

time,

high

ground

schematic

presented

at

Taniguchi

hybridization

[4,51, the

polarization

in

wurtzite

inclusion

how the valence

for

3d6

the

with

suggest

constructed by

in

Fe

between

diagram

shows

the

G I$

maximum

in the BZ,

of

.n

to

of states

4.34

---

excited

be

E,A,

_--

structure

which

4.46

0.71

splittings

electron

----

5.47l'

existence

one

4.10

C

interaction

and

E,A,

__

configuration

type

a

E,A

[3l,and

the

2 1 Z slope b [eV]

_--

in the

spin

CdFeSc

5.0"

reflectivity

the

This work CdSe

E;

according

cl

[ill

--

The energy

level

Phillips

_--

-_-

the

and [lOI

__-

Large reg. including

interband

range

5.00

Region around

1)

and CdFeSe

V4 - V,

Msc.p.at

b)

Harbeke

Region BZ

of the CdSe

of c' 1 E+ polarization

4 - 10 eV energy

r121

M,c.p.at

I

positions

in

Vol. 70, No. 7

could atomic

interactions

conclusion

we

have

ascertained

that:

(i) that

The we

eflecttivity measured

spectrum

in 4

-

10 eV

of

CdSe

energy

,VOl.

70,

No.

697

Cdl_xFexSe ROOM TEMPERATURE

7

linearly

shifted

content.

Simultaneously

are

I

observed

stronger Fe 3d

near Ion Fez’

the

top

observed

Cd Fe Se

Slater splitting

band

(iv)

Fig.Z.One

Fe2+

3d

schematic

of

the valence of

in

the

density

contribution

of

band

CdSe,

A

C

CdFeSe

(a)

states

- an

(DOS) (b),

results

3d

ternary the

theoretical

experimental

expectations

band

structure

of

the

calculations

(Tab.1). (ii)

In

CdFeSe

reflectivity

mixed

structure

spectra

compounds

observed

in

the

pure

crystal

electrons

the

diagram

is

compounds. available

and an influence

of

field

on

schematic the

hybridization

the

of

Fe

splitting been

has

3d

electron

one

and

suggested

(Fig.2).

ACKNOWLEDGMENTS thank

the

della

Lute the

and

of rich

CdSe

is

would

per

and

sample

Structtura

della

partial

preparation

Group

thank

also

for

for X-ray

acknowledges

to

(PULS)

We

B.Orlowski

orientation.

like

l'utilizazzione

di Sinchrotrone

M.Colapietro

the

for

We

-

Programma

hospitality.

'B.Velicky

also the

results

as

and

electrons,

previous

and

similarly

for HgFeSe

cubic

for confirms

VBM

the

feature

B

respectively.

range,

of

in

additional

expected

nonhybridized Fe

of

of the

for CdFeSe

and

of

hybridized

diagram

hybridization

electrons

expected

- DOS

the

and

and

an

(b)

electron

splitting

the

expected

is DOS

and

Fe 3d orbitals

and

considering

experimental (a)

about

Se 4p

between

Cd 5p

therefore

and

valence

of the BZ

informs

result

interaction

than

blurring identified

to. it.

above

(iii)

of Fe

structures

strong

at the F point

or very close m

these

for all maxima

as transitions

u

the increase

Particular

blurred.

was

with

One

the

discussion diagnose of us

Instituto

Materia

CNR,

financial

of

(A.K) di

Frascati during

support

of this work.

REFERENCES

1.

R.R.Galazka

in

Semiconductors

ed.

Bristol

1979,

International

Franciosi, R.Reifenberger, Sci.Technol.,

of

3.

B.L.H.Wilson, 133;

p. Conf.on

Phys., Stockholm, 2.

Physics

18-th

Semicon

S.Haug,

ductor

Baranowski,

U.Debska, A3(3),

926

Phys.,

C.Caprile, J.Vac,

(1985),

B.OrIowski,

H.Arciszewska,

1986 p.1727, 4.

P.Dzwonkowski,

A.Mycielski, B.Kowalski,

Paramagnetic Ions,

J.Phys.

19, 3605

A.Abragam

M.Dobrowolska,

W.Dobrowolski,

and

Solid

State

(19861, B.Blaney,

Resonance

Clarendon

C.

and J.M.

Press,

Electron

of Transition Oxford

1970,

Cdl_xFexSe ROOM TEMPERATURE

698

5. A.Zunger,

Solid

State

Phys.

39,

275

S.Chang,

P.Philip,

A.Franciosi,

8.

M

Taniguchi,

J.Ghijsen,

and

(1986),

A.Sarem,

M.Cardona

Phys.

K.Jezierski,

B.A.Orlowski, Phys.Pol.

Rev.

J.Misiewicz,

137, Al467

and

N.Zema

-

(19641, lB.T.K.Bergstresser Rev.

164,

G.Harbeke

1069

Phys.

Phys.

(1985),

Pastori-Paravicini,

Electronic

States Pergamon

and

Optical

Press,

Oxford

J.Oleszkiewicz,

Rev.

Phys.

A.Rodzik,

J. Phys.

20, 5601

C

(19871,

N.Zema :Solid

and State

and references

therein, Rev.

133,

and M.L.Cohen, (1967),

ibid 31, 7526 and

Transitions,

A.Mycielski,

(1965),

ll.J.C.Phillips,

(1984);

Rev. B,30,

lG.A.Kisiel,M.Piacentini,F.Antonangeli,

M.Piacentini,

not published lO.M.Cardona

and

Phys.

1975

Acta

in press,

9. F.Antonangeli,

2295

A,Kisiel,

M.PodgOrny,

M.Zimnal-Starnawska,

B.J.Kowalski,

A.Mycielski

M.T.CzyZyk,

N.Motta,

15.F.Bassani

J.Bak-Misiak,

S.H.Volz,

Rev. B, 28, 935

(19831,

R.L.Johnson,

L.Ley,

O.F.Sankey,

Phys.

14.A.Balzarotti,

A - in press,

B.33,

1206

C.Caprile,

R.Reifenberger,

J.Vac.Sci.Technol. 7.

Kobayasi,

and J.D.Dow,

(19861, 6. A.Wall,

13.Akido

Vol. 70, No. 7

A452

Phys.

17.F.Orlowski

- private

communication